1. Field of the Invention
The invention relates to a positive electrode active material for a non-aqueous secondary battery, and to a non-aqueous lithium secondary battery.
2. Description of Related Art
Complex oxides of layered structure formed of a combination of lithium, nickel and manganese are being examined as positive electrode active material for non-aqueous lithium secondary battery. For instance, in the lithium nickel complex oxides, when the full widths at half maximum of the diffracted peaks at planes (003) and (104) in the Miller indices hid of a powder X-ray diffraction using CuKα beam are respectively FWHM(003) and FWHM(104) and the integrated intensities of the diffraction peaks are defined as I(003) and I(104) respectively, those satisfying 0.75≦FWHM(003)/FWHM(104)≦0.9 and 0.25≦I(104)/I(003)≦0.9 are proposed to be desirable as positive electrode active materials (for instance, see Japanese Patent Application Publication No. 2000-195514 (JP 2000-195514 A)). As a reason for this, FWHM(003)/FWHM(104) is an index of the c-axis orientation and the ratio of integrated intensities I(104)/I(003) is an index of contamination of Ni ions into Li ion sites and reactivity of the active material and the electrolytic solution. That is to say, if FWHM(003)/FWHM(104) becomes small, while the c-axis orientation in the trigonal system becomes higher, if it falls outside the range described above, it is not desirable from the points of view of crystal growth in a direction perpendicular to the c-axis, and extension and contraction in the c-axis direction. In addition, in case I(104)/I(003) exceeds 0.9, because large amounts of Ni ions contaminate the Li ion sites, the amount of Li ions that can be stored/released diminishes while at the same time the large current charge-discharge characteristics decrease. Therefore, it is not desirable as a positive electrode active material. If I(104)/I(003) becomes less than 0.25, because the active material and the electrolytic solution tend to react. Therefore, it is not desirable as a positive electrode active material.
In addition, Li[Lix(Ni1/2Mn1/2)1−x]O2 (0≦x≦0.3), which is an oxide with a layered structure formed of a combination of lithium, nickel and manganese, in which the errors in the proportions of nickel and manganese are within 10 atom % has been proposed as a positive electrode active material (for instance, see WO2002/078105). Here, a positive electrode active material that satisfies I(003)/I(104)<1 for the integrated intensity ratio of the X-ray diffraction peaks assigned to the Miller indices (003) and (104) is deemed desirable.
However, with the non-aqueous lithium secondary battery of the JP 2000-195514 A described above, while capacity increase, or the like, was intended by taking the integrated intensity ratio, or the like, of the X-ray diffraction peaks into consideration, it was still not sufficient. For instance, with car batteries, or the like, in addition to the capacity deterioration being small even if repeatedly charged-discharged in temperature conditions from a low temperature on the order of −30° C. to a high temperature on the order of 60° C., the internal resistance increase of the battery needs to be kept small. Thus, a further improvement of the output characteristics of the battery was sought.